Single click host maintenance

ABSTRACT

Techniques to facilitate virtual machine (VM) host maintenance are disclosed. A host requiring maintenance is converted to a VM running on another host which satisfies certain requirements, such as having sufficient resources and the same network connectivity as the host requiring maintenance. As part of this physical-to-virtual conversion, or after said conversion, the VM may be synchronized to the host requiring maintenance, such that the CPU state and memory contents of the VM and host are identical. Active control may then be passed to the VM, and the host powered down for the maintenance. After maintenance is completed and the host powered back on, virtual-to-physical conversion may be applied to convert the VM back to the host. The host may then be synchronized to the VM, and active control passed back to the host.

BACKGROUND

Computer virtualization is a technique that involves encapsulating aphysical computing machine in a virtual machine (VM) that is executedunder the control of virtualization software running on a hardwarecomputing platform, or “host.” A group of hardware computing platformsmay be organized as a cluster to provide resources for VMs. In a datacenter, it is common to virtualize hundreds, even thousands of VMsrunning on multiple clusters of host servers.

At times, a host running a set of VMs may undergo maintenance, includingreplacing faulty hardware components, replacing out-of-warranty hardwarecomponents with new components, upgrading firmware, upgrading installedsoftware and applications, physically moving hardware, and installingnew hardware components, among other things. Such maintenance canrequire VMs running on the host to be stopped, i.e., require VMdowntime. One approach for eliminating such downtime uses live migrationto move the VMs onto other hosts, after which maintenance is performed,and migrating the VMs back to the original host. Typically, thisrequires a system administrator to manually select migration targets toensure that network connectivity and other resources needed by the VMsare not disrupted by the live migrations. This can be informationintensive and tedious, as a large number of VMs (e.g., 100s) may run onthe host server. Further, the system administrator may have to keeptrack of the migrated VMs and move those VMs back to the original hostafter the maintenance is performed.

SUMMARY

Embodiments presented herein provide techniques for virtual machine hostmaintenance. The techniques include receiving a selection of a firsthost system hosting at least a first VM, the first host system being aphysical computing server which requires maintenance. The techniquesfurther include identifying a second host system which satisfiesrequirements for performing a physical-to-virtual conversion of thefirst host system to a first VM running on the second host system. Inaddition, the techniques include performing the physical-to-virtualconversion of the first host system to the first VM, passing activecontrol from the first host system to the first VM, and shutting downthe first host system for the maintenance.

Further embodiments of the present invention include a computer-readablestorage medium storing instructions that when executed by a computersystem cause the computer system to perform one or more of thetechniques set forth above, and a computer system programmed to carryout one or more of the techniques set forth above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a block diagram of a server utilizing a virtualizationarchitecture.

FIG. 2 illustrates a user interface for selecting a host which requiresmaintenance, according to an embodiment.

FIG. 3 illustrates an approach for single-click host maintenance,according to an embodiment.

FIG. 4 illustrates a method for performing host maintenance, accordingto an embodiment.

DETAILED DESCRIPTION

Embodiments presented herein provide techniques to facilitate virtualmachine (VM) host maintenance. In one embodiment, the host requiringmaintenance is converted to a VM running on another host which satisfiescertain requirements for the conversion, including having sufficientresources and the same network connectivity as the host requiringmaintenance. In general, physical-to-virtual conversions may includemigrating the host's operating system, applications, and data to the VM.In one embodiment, the physical-to-virtual conversion may includemigrating a hypervisor of the host and VMs running on the hypervisor,which may be treated as applications for purposes of the migration. Aspart of the physical-to-virtual conversion, or after said conversion,the VM to which the host is converted may be synchronized to the hostitself, such that the CPU state and memory contents of the VM and hostare identical. Active control may then be passed to the VM, and the hostcan be powered down for maintenance. After completing the maintenanceand powering the host back on, virtual-to-physical conversion may beapplied to convert the VM back to the host. The host may then besynchronized to the VM to which the host was previously converted, andactive control passed from the VM to the host.

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention.However, it will be apparent to one skilled in the art that the presentinvention may be practiced without some of these specific details. Inother instances, well known process operations and implementationdetails have not been described in detail in order to avoidunnecessarily obscuring the invention.

FIG. 1 illustrates a block diagram of a virtualized computer system 100with which one or more embodiments of the present invention may beutilized. As illustrated, virtualized computer system 100 includes oneor more host computers 101 _(1-N) and a virtual machine managementsystem 124. For clarity, only a first host computer 101 ₁ is shown indetail.

Host computers 101 _(1-N) are configured to support virtualizedenvironments and to deliver one or more application services related toinformation technology, including but not limited to, web services,database services, data processing services, and directory services. Inlarger systems, a plurality of host computers 101 _(1-N) may form a datacenter. Each of host computers 101 _(1-N) provides a virtualizationlayer that abstracts processor, memory, storage, and/or networkingresources into multiple virtual machines (VMs) that run concurrentlythereon.

Illustratively, host computer 101 ₁ includes conventional components ofa computing device, such as a memory 130, a processor 132, a diskinterface 134, and a network interface 136. Disk interface 134, whichmay be a “host bus adapter” (HBA), connects host computer 104 to storagedevices such as a storage area network (SAN) device 110. Networkinterface 136, which may be a “network interface controller” (NIC),connects host computer 104 to a network and in some embodiments, tostorage devices, such as a network attached storage (NAS) device.

As shown, one or more virtual machines VMs 108 _(1-N) are configuredwithin host computer 101 ₁, and share the hardware resources of hostcomputer 101 ₁. The virtual machines run on top of a software interfacelayer 140 ₁ (also referred to herein as a “hypervisor”) that enablessharing of the hardware resources of host computer 101 ₁ by the VMs 108_(1-N). Hypervisor 140 ₁ may run on top of the operating system of hostcomputer 101 ₁ or directly on hardware components of host computer 101₁. As also shown, each VM 108 _(1-N) has a corresponding virtual machinemonitor (VMM) 120 _(1-N), provided in hypervisor 104 ₁, that provides avirtual hardware platform for corresponding VMs. For clarity, only afirst VMM 120 ₁ is shown in detail. As shown, emulated hardware of VMM120 ₁ includes a virtual processor 122, a virtual memory 124, a virtualdisk 126, and a virtual NIC 128.

Each VM 108 _(1-N) may include a guest operating system (OS) and one ormore guest applications running on top of the guest OS. As shown, VM 108₁ includes guest OS 110 and applications 112 running thereon. Usingphysical-to-virtual conversion, the operating system, applications, anddata of a physical computing system may be migrated to a VM. That is,the physical computing system may be converted to a VM. Publiclyavailable physical-to-virtual conversion tools include VMware® vCenter™Converter™. In one embodiment, physical-to-virtual conversion may beused to convert a VM host (e.g., one of hosts 101 _(1-N)) that requiresmaintenance to a VM running on another VM host that has sufficientresources and the same network connectivity as the converted VM host.During such a conversion, the VMs running on the host may be treated asapplications, and their states copied to the other host. Illustratively,VM 108 _(N) includes a migrated hypervisor 105, on which VMs 109 _(1-N)run. Such a VM may also be synchronized to the host requiringmaintenance, and active control passed to the VM so that the host may bepowered down for maintenance. After the maintenance is completed and thehost is powered back on, the contents of the VM may then be transferredback to the physical host using virtual-to-physical conversion, which isessentially the opposite of physical-to-virtual conversion. The physicalhost may then be synchronized with the VM, and active control passedback to the host.

VM management center 140 is a computer program in communication witheach of host computers 101 _(1-N) that carries out administrative tasksfor virtualized computer system 100, such as managing the hostcomputers, managing the virtual machines running within each hostcomputer, provisioning the virtual machines, migrating virtual machinesfrom one host computer to another, physical-to-virtual andvirtual-to-physical conversions, allocating physical resources, such asprocessor and memory, load balancing between host computers, and so on.In one embodiment, VM management center 140 may reside and execute incentral server(s). In an alternative embodiment, VM management center140 may instead execute on one of host computers 101 _(1-N) as a virtualmachine. In a particular embodiment, VM management center 140 may beVMware® vCenter™. In another embodiment, VM management center 140 mayabstract and pool resources managed by multiple management programs,each of which performs administrative tasks for a respective set of hostcomputers, so that users may, e.g., create, use, and manage VMs hostedon any of the host computers via a web interface. For example, VMmanagement center 140 may be a VMware vCloud® Director™.

As noted, VM management center 140 may perform administrative tasks forvirtualized computer system 100 autonomously, or may performadministrative tasks in response to commands issued by a systemadministrator. As described in greater detail below, a management module145 of VM management center 140 may perform various functions duringhost maintenance, including identifying another host to which the hostrequiring maintenance may be transferred via a physical-to-virtualconversion, physical-to-virtual conversion of the host requiringmaintenance, synchronizing the VM to which the host was converted to thehost itself, and virtual-to-physical conversion of the VM back to thehost after the maintenance. Management module 145 may further includeinstructions that present a graphical user interface or a command-lineinterface to the system administrator. In one embodiment, the interfacepresented by management module 145 may permit a host requiringmaintenance to be selected with a single click as depicted in FIG. 2,which illustrates a user interface 200 for selecting the host requiringmaintenance.

As shown, interface 200 is a graphical user interface which presentsicons representing hosts managed via VM management center 140. Byhovering mouse pointer 210 over one of the icons and clicking on theicon, a system administrator may indicate that maintenance is to beperformed on the host associated with that icon. Upon receiving such amouse click, management module 145 may identify another host to whichthe selected host may be transferred via a physical-to-virtualconversion, and perform said physical-to-virtual conversion to convertthe selected host to a VM running on the other host. Note, if more thanone host is identified, the physical-to-virtual conversion mayautomatically be performed to a most suitable of the identified hosts(based on, e.g., the host having the most free resources, or some othercriteria). For example, VM management center 140 may provide, to thesystem administrator, an option to automatically convert selected hoststo the most suitable of identified hosts. Alternatively, user interface200 may be made to display the multiple identified hosts, giving thesystem administrator a choice of which host to perform thephysical-to-virtual conversion to. If, on the other hand, no hosts aresuccessfully identified for the physical-to-virtual conversion, userinterface 200 may be made to display an error message indicating thatmaintenance cannot be performed currently. In one embodiment, the errormessage may also include the reason why maintenance cannot be performed(e.g., no target for a physical-to-virtual conversion was identified).

As part of, or after, the physical-to-virtual conversion, managementmodule 145 may synchronize the VM running on the other host to theselected host. Management module 145 may then transfer active control tothe VM and power down the selected host. Thereafter, maintenance may beperformed on the selected host to, e.g., replace faulty hardwarecomponents, replace out-of-warranty hardware components, upgradefirmware, physically move hardware, install new hardware components,upgrade installed software and applications, etc. After the maintenanceis completed, management module 145 may identify, or be notified, whenthe selected host original host is powered back on. Management module145 may then perform a virtual-to-physical conversion of the VM back tothe selected host, synchronize that host to the VM, and transfer activecontrol to the host.

FIG. 3 illustrates an approach for single-click host maintenance,according to an embodiment. As discussed, management module 145 runningon VM management center 140 may provide a user interface which permits asystem administrator to indicate a VM requiring maintenance.Illustratively, assume host 101 _(N) has been indicated by the systemadministrator as requiring maintenance using, e.g., the user interfacedepicted in FIG. 2. For example, a hardware component may be faulty orout-of-date, requiring physical intervention to replace the component.Management module 145 may then identify an available host to which totransfer the host 101 _(N) using physical-to-virtual conversion. In oneembodiment, the host may be identified as one having sufficientresources (e.g., memory, network bandwidth, etc.) and the same networkconnectivity as the host requiring maintenance, where having the samenetwork connectivity includes being connected to the same physicalswitches (e.g., hosts 101 ₂₋₃ are connected to the same switches 300₃₋₄). The requirements of having sufficient resources and the samenetwork connectivity ensure that the physical-to-virtual conversion canbe performed and VMs running on the host will not suffer disruptions asa result of said conversion. For example, the host may be a developmentserver requiring a large quantity of memory (e.g., 1 Tb of memory), andthe management module 145 may identify another host having at least thatamount of free memory. As another example, VMs running on the host mayrequire high network bandwidth (e.g., 10 Gb network connectivity), andthe management module 145 may identify another host which can providesuch bandwidth.

After successfully identifying the other host, management module 145 mayconvert the host requiring maintenance to a VM running on the host. Asnoted above, if multiple hosts are identified, physical-to-virtualconversion may automatically be performed to a most suitable of theidentified hosts. Alternatively, the multiple identified hosts may bepresented to a system administrator via a user interface, giving thesystem administrator a choice of candidate hosts to perform thephysical-to-virtual conversion to. If, on the other hand, no hosts aresuccessfully identified, then an error message may be displayedindicating that maintenance cannot be performed currently, as well asthe reason.

During the physical-to-virtual conversion itself, the VMs of theoriginal host may be treated as applications running on the hypervisorand have their states copied to the new host, similar to applicationsrunning on operating systems being migrated in typicalphysical-to-virtual conversions. Management module 145 itself mayperform this conversion, or invoke a physical-to-virtual conversion toolsuch as the VMware® vCenter™ Converter™ tool. As shown, host 101 ₃ isconverted to VM 108 running on host 101 ₂. Management module 145 mayalso synchronize VM 108 and host 101 ₃. The synchronization of VM 108with host 101 ₃ may include capturing processor and memory transitionson host 101 ₃ as events, and applying those transitions to VM 108 inreal time. That is, operation(s) performed on host 101 ₃ are alsoperformed on VM 108, such that the CPU state and memory contents of host101 ₃ and VM 108 are identical. A number of processors, includingcertain processors available from Intel Corp. and Advanced MicroDevices, Inc., provide hardware support for such synchronization. VM 108and host 101 ₃ may be synchronized as part of the physical-to-virtualconversion, or after it. In a particular embodiment, VMware® vLockstep™may be invoked to synchronize VM 108 with host 101 ₃.

After the physical-to-virtual conversion and synchronization, host 101 ₃is in an active state in which actual processing is performed by host101 ₃, whereas VM 108 is in a passive state that mirrors activity inhost 101 ₃. Management module 145 may transfer active control to VM 108.That is, VM 108 is brought into an active state and performs actualprocessing. At substantially the same time, management module 145 maybring host 101 ₃ to a passive state mirroring VM 108. Then, managementmodule 145 may power off host 101 ₃ so that maintenance may be performedthereon. After maintenance is completed and host 101 ₃ powered back on,management module 145 may identify that host 101 ₃ is running andconvert VM 108 back to host 101 ₃ using virtual-to-physical conversion.Similar to physical-to-virtual conversion, virtual-to-physicalconversion may generally include migrating the operating system,applications, and data of a VM to a physical computing system. Suchmigration in the context of VM hosts may include migrating thehypervisor and VMs running thereon from the VM (e.g., VM 108) to thehost (e.g., host 101 ₃). Host 101 ₃ and VM 108 may be synchronized aspart of the physical-to-virtual conversion, or after said conversion.Active control may then be passed back to host 101 ₃.

FIG. 4 illustrates a method for performing host maintenance, accordingto an embodiment. As shown, the method 400 begins at step 410, where ahost management module receives a selection of a first host on whichmaintenance is to be performed. In one embodiment, the selection may beas simple as a single click on a user interface, indicating the firsthost as requiring maintenance.

At step 411, the management module identifies a second host thatsatisfies requirements for a physical-to-virtual conversion of the firsthost. In one embodiment, the requirements may include having sufficientresources and the same network connectivity as the first host. Again,having sufficient resource may include the second host having adequatefree memory, network bandwidth, etc., depending on the circumstances.Network connectivity requirements may include identifying a hostconnected to the same physical switches. As discussed, theserequirements ensure the physical-to-virtual conversion can be performedsuccessfully and VMs running on the host will not suffer disruptions asa result of said conversion.

If identification of the second host at step 411 is unsuccessful (i.e.,no second host can be identified), then at step 413, the managementmodule issues an error message notifying the system administrator that,currently, host maintenance for the selected host cannot be performed.In one embodiment, the management module may also issue additionaldetails indicating the reason host maintenance cannot be performed. Forexample, the error message may state that no secondary host could befound for a physical-to-virtual conversion.

If, on the other hand, a second host is successfully identified at step411, the management module converts the first host into a VM running onthe second host at step 412. This physical-to-virtual conversion mayinclude migrating the hypervisor and VMs of the first host to the VMrunning on the second host, and may be performed by the managementmodule itself or by a conversion tool (e.g., VMware® vCenter™Converter™) invoked by the management module. As part of thephysical-to-virtual conversion, or after said conversion, the managementmodule may synchronize the VM running on the second host to the firsthost. As discussed, synchronizing the VM to the first host may includecapturing processor and memory transitions on the first host as events,and applying those transitions to the VM in real time so that the CPUstate and memory contents of the VM and first host are identical. In aparticular embodiment, VMware® vLockstep™ may be invoked to synchronizethe VM with the host. As previously noted, multiple hosts may beidentified for the physical-to-virtual conversion, in which case theconversion may automatically be performed to a most suitable of theidentified hosts (e.g., based on the host having the most freeresources, or some other criteria). Alternatively, the multipleidentified hosts may be presented to a system administrator via a userinterface, giving the system administrator a choice of candidate hoststo perform the physical-to-virtual conversion to.

At step 414, active control is passed from the first host to the VMrunning on the second host. Here, the management module may bring the VMinto an active state in which the VM performs actual processing.Additionally, the management module may bring the first host to apassive state in which the host mirrors the activity of the VM.

Then, at step 415, the management module powers down the first host toenable maintenance to be performed thereon. Any feasible type ofmaintenance may be performed, including replacing faulty hardwarecomponents, replacing out-of-warranty hardware components, upgradingfirmware, physically moving hardware, installing new hardwarecomponents, upgrading installed software and applications, etc.

After the maintenance is completed and the first host is powered backon, the management module may detect, or be notified, that the firsthost has been powered back on and, at step 416, transfer the VM runningon the second host back to the first host using virtual-to-physicalconversion. Such virtual-to-physical conversion may include migratingthe hypervisor and VMs running thereon from the VM running on the secondhost to the first host. The first host may also be synchronized to theVM as part of the physical-to-virtual conversion, or after saidconversion. Then, at step 418, active control is returned to the firsthost.

Advantageously, embodiments described herein permit automatic transferof VMs from a host that requires maintenance to another host, which maybe initiated by a single click in some embodiments. No VM downtime issuffered, and the system administrator need not manually migrate VMsbefore the maintenance, keep track of the migrated VMs, or migrate thoseVMs back to the original host after maintenance is completed.

The various embodiments described herein may employ variouscomputer-implemented operations involving data stored in computersystems. For example, these operations may require physical manipulationof physical quantities—usually, though not necessarily, these quantitiesmay take the form of electrical or magnetic signals, where they orrepresentations of them are capable of being stored, transferred,combined, compared, or otherwise manipulated. Further, suchmanipulations are often referred to in terms, such as producing,identifying, determining, or comparing. Any operations described hereinthat form part of one or more embodiments of the invention may be usefulmachine operations. In addition, one or more embodiments of theinvention also relate to a device or an apparatus for performing theseoperations. The apparatus may be specially constructed for specificrequired purposes, or it may be a general purpose computer selectivelyactivated or configured by a computer program stored in the computer. Inparticular, various general purpose machines may be used with computerprograms written in accordance with the teachings herein, or it may bemore convenient to construct a more specialized apparatus to perform therequired operations.

The various embodiments described herein may be practiced with othercomputer system configurations including hand-held devices,microprocessor systems, microprocessor-based or programmable consumerelectronics, minicomputers, mainframe computers, and the like.

One or more embodiments of the present invention may be implemented asone or more computer programs or as one or more computer program modulesembodied in one or more computer readable media. The term computerreadable medium refers to any data storage device that can store datawhich can thereafter be input to a computer system—computer readablemedia may be based on any existing or subsequently developed technologyfor embodying computer programs in a manner that enables them to be readby a computer. Examples of a computer readable medium include a harddrive, network attached storage (NAS), read-only memory, random-accessmemory (e.g., a flash memory device), a CD (Compact Discs)—CD-ROM, aCD-R, or a CD-RW, a DVD (Digital Versatile Disc), and other optical andnon-optical data storage devices. The computer readable medium can alsobe distributed over a network coupled computer system so that thecomputer readable code is stored and executed in a distributed fashion.

Although one or more embodiments of the present invention have beendescribed in some detail for clarity of understanding, it will beapparent that certain changes and modifications may be made within thescope of the claims. Accordingly, the described embodiments are to beconsidered as illustrative and not restrictive, and the scope of theclaims is not to be limited to details given herein, but may be modifiedwithin the scope and equivalents of the claims. In the claims, elementsand/or steps do not imply any particular order of operation, unlessexplicitly stated in the claims.

Virtualization systems in accordance with the various embodiments, maybe implemented as hosted embodiments, non-hosted embodiments or asembodiments that tend to blur distinctions between the two, are allenvisioned. Furthermore, various virtualization operations may be whollyor partially implemented in hardware. For example, a hardwareimplementation may employ a look-up table for modification of storageaccess requests to secure non-disk data.

Many variations, modifications, additions, and improvements arepossible, regardless the degree of virtualization. The virtualizationsoftware can therefore include components of a host, console, or guestoperating system that performs virtualization functions. Pluralinstances may be provided for components, operations or structuresdescribed herein as a single instance. Finally, boundaries betweenvarious components, operations and data stores are somewhat arbitrary,and particular operations are illustrated in the context of specificillustrative configurations. Other allocations of functionality areenvisioned and may fall within the scope of the invention(s). Ingeneral, structures and functionality presented as separate componentsin exemplary configurations may be implemented as a combined structureor component. Similarly, structures and functionality presented as asingle component may be implemented as separate components. These andother variations, modifications, additions, and improvements may fallwithin the scope of the appended claims(s).

I claim:
 1. A computer-implemented method, comprising: receiving aselection of a first host system hosting at least a first VM, whereinthe first host system is a physical computing server which requiresmaintenance; identifying a second host system which satisfiesrequirements for performing a physical-to-virtual conversion of thefirst host system to a first VM running on the second host system;performing the physical-to-virtual conversion of the first host systemto the first VM; passing active control from the first host system tothe first VM; and shutting down the first host system for themaintenance.
 2. The computer-implemented method of claim 1, wherein therequirements for performing the physical-to-virtual conversion includethe second host system having sufficient computing resources.
 3. Thecomputer-implemented method of claim 1, wherein the requirements forperforming the physical-to-virtual conversion include the second hostsystem having a network connectivity state matching a correspondingnetwork connectivity state of the first host system.
 4. Thecomputer-implemented method of claim 1, further comprising, after, or aspart of, performing the physical-to-virtual conversion, synchronizingthe first VM with the first host system.
 5. The computer-implementedmethod of claim 1, further comprising, after the maintenance isperformed on the first host system: powering on the first host system;performing a virtual-to-physical conversion of the first VM to the firsthost system; synchronizing the first host system with the first VMafter, or as part of, the virtual-to-physical conversion; and passingactive control from the first VM to the first host.
 6. Thecomputer-implemented method of claim 1, wherein the selection of thefirst host system is performed via a mouse click.
 7. Thecomputer-implemented method of claim 1, further comprising, ifidentification of the second host is unsuccessful, displaying anotification that maintenance cannot currently be performed.
 8. Anon-transitory computer-readable storage medium embodying computerprogram instructions for performing operations comprising: receiving aselection of a first host system hosting at least a first VM, whereinthe first host system is a physical computing server which requiresmaintenance; identifying a second host system which satisfiesrequirements for performing a physical-to-virtual conversion of thefirst host system to a first VM running on the second host system;performing the physical-to-virtual conversion of the first host systemto the first VM; passing active control from the first host system tothe first VM; and shutting down the first host system for themaintenance.
 9. The computer-readable storage medium of claim 8, whereinthe requirements for performing the physical-to-virtual conversioninclude the second host system having sufficient computing resources.10. The computer-readable storage medium of claim 8, wherein therequirements for performing the physical-to-virtual conversion includethe second host system having a network connectivity state matching acorresponding network connectivity state of the first host system. 11.The computer-readable storage medium of claim 8, the operations furthercomprising, after, or as part of, performing the physical-to-virtualconversion, synchronizing the first VM with the first host system. 12.The computer-readable storage medium of claim 8, the operations furthercomprising, after the maintenance is performed on the first host system:powering on the first host system; performing a virtual-to-physicalconversion of the first VM to the first host system; synchronizing thefirst host system with the first VM after, or as part of, thevirtual-to-physical conversion; and passing active control from thefirst VM to the first host.
 13. The computer-readable storage medium ofclaim 8, wherein the selection of the first host system is performed viaa mouse click.
 14. The computer-readable storage medium of claim 8, theoperations further comprising, if identification of the second host isunsuccessful, displaying a notification that maintenance cannotcurrently be performed.
 15. A system, comprising: a processor; and amemory, wherein the memory includes a program for reducing perceivedread latency, the program being configured to perform operationscomprising: receiving a selection of a first host system hosting atleast a first VM, wherein the first host system is a physical computingserver which requires maintenance, identifying a second host systemwhich satisfies requirements for performing a physical-to-virtualconversion of the first host system to a first VM running on the secondhost system, performing the physical-to-virtual conversion of the firsthost system to the first VM, passing active control from the first hostsystem to the first VM, and shutting down the first host system for themaintenance.
 16. The system of claim 15, wherein the requirements forperforming the physical-to-virtual conversion include the second hostsystem having sufficient computing resources.
 17. The system of claim15, wherein the requirements for performing the physical-to-virtualconversion include the second host system having a network connectivitystate matching a corresponding network connectivity state of the firsthost system.
 18. The system of claim 15, the operations furthercomprising, after, or as part of, performing the physical-to-virtualconversion, synchronizing the first VM with the first host system. 19.The system of claim 15, the operations further comprising, after themaintenance is performed on the first host system: powering on the firsthost system; performing a virtual-to-physical conversion of the first VMto the first host system; synchronizing the first host system with thefirst VM after, or as part of, the virtual-to-physical conversion; andpassing active control from the first VM to the first host.
 20. Thesystem of claim 15, wherein the selection of the first host system isperformed via a mouse click.